Ventilator monitor and alarm apparatus are used for monitoring a patient or user breathing in a ventilator circuit, and to create an alarm when patient breathing falls below or rises above preselected desired minimum or maximum pressure, respectively. One such device for monitoring patient ventilator circuit breathing and alarming when pressure falls below a preselected minimum is disclosed in U.S. Pat. No. 4,803,471. The apparatus disclosed in that patent also includes an automatic on feature which turns the apparatus on, independent of an on/off switch when the device senses the preselected minimum pressure in the breathing circuit. However, in the aforesaid prior art apparatus, if the therapist, nurse or person operating the device sets the preselected minimum pressure too low, although the unit is turned on by the patient's first breath, it would not alarm where the sensed ventilator pressure is above the preselected minimum, regardless of the patient's breathing cycle pressure. For example, the ventilator circuit tubing may be crimped, occluded or the circuit otherwise malfunctioning, but with a sensed circuit pressure higher than the preselected minimum pressure an alarm condition is prevented from occurring. On the other hand, in such an apparatus, if the preselected minimum is set too high, the device would not be automatically turned on since the automatic on function only operates when the circuit pressure passes through the preselected minimum for the first time.
In yet another ventilator circuit monitoring and alarm apparatus disclosed in U.S. Pat. No. 4,316,182, the automatic on feature is not provided with any adjustment for selecting a desired minimum pressure. Since there is no adjustment of the minimum pressure, although the apparatus monitors the patient's breathing cycle, if the pressure of the patient's first breath is not enough to close a breath detection switch, the unit will not be turned on. In addition, a patient having a very low or shallow breathing pressure cycle might not create an alarm condition.